Barbara Bush, 1925-2018

First lady Barbara Bush poses with her dog Millie in 1990.

U.S. President George W. Bush (R) waves alongside his parents, former President George Bush and former first lady Barbara Bush upon their arrival Fort Hood, Texas, April 8, 2007.

FILE - In this 1964 file photo, George H.W. Bush sits on couch with his wife Barbara and their children. George W. Bush sits at right behind his mother. Behind couch are Neil and Jeb Bush.

FILE - In this Jan. 17, 2003 file photo, former first ladies get together for a group photo at a gala 20th anniversary fundraising event saluting Betty Ford and the Betty Ford Center in Indian Wells, Calif.

FILE- In this March 21, 2011, file photo, from left, former President Bill Clinton, former President George H.W. Bush and his wife Barbara Bush stand for the National Anthem at the Kennedy Center.

FILE - In this Nov. 19, 1992 file photo, first lady Barbara Bush greets first lady-to-be Hillary Clinton upon her arrival at the White House in Washington.

President Barack Obama stands with first lady Michelle Obama, left, former president George W. Bush, Laura Bush, and Barbara Bush at the dedication of the George W. Bush presidential library on the campus of Southern Methodist University in Dallas, April

President George W. Bush, right, sits with, from left, his brother Neal Bush; his mother, former first lady Barbara Bush; his wife first lady Laura Bush; and father, former President George H.W. Bush, as they take part in a reception in honor of the Point

Former first ladies Barbara Bush, left, and Laura Bush, take part in the Enduring Legacies of America’s First Ladies conference, Nov. 15, 2012, in Austin, Texas.

Barbara Bush, center, jokes with her son, Republican presidential candidate, former Florida Gov. Jeb Bush, while introducing him at a town hall meeting at West Running Brook Middle School in Derry, N.H., Feb. 4, 2016.

Former President George H.W. Bush and wife, Barbara, wave as they arrive on the field for a coin toss before the NFL Super Bowl 51 football game between the Atlanta Falcons and the New England Patriots, Feb. 5, 2017, in Houston.

Former first lady Barbara Bush uses a walker as she leaves a luncheon at the Kennebunk River Club on her 90th birthday, June 8, 2015, in Kennebunkport, Maine.

FILE - Former first lady Barbara Bush listens to her son, President George W. Bush, as he speaks on Social Security reform in Orlando, Florida, March 18, 2005.